Beam shape compensation optical system

Details Beam shape compensation optical system Beam shape compensation optical system

2000-01-06

2001-04-17

Spyrou, Cassandra (Department: 2872)

Optical: systems and elements

Light control by opaque element or medium movable in or...

With rotating or pivoting element

C359S290000, C359S837000

Reexamination Certificate

active

06219169

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a beam shape compensation optical system for compensating a cross-sectional shape of a beam, and an imaging device employing the beam shape compensation optical system.
Among devices utilizing light beams, some require a beam of which a cross sectional shape is compensated. For example, in an imaging device utilizing a scanning beam, it is preferable that a beam spot formed on a surface on which an image is formed has a circular shape. Therefore, the cross-sectional shape of a beam emitted by a light source such as an argon laser source is compensated to have a circular cross section.
Conventionally, such compensation is done at a designing and/or manufacturing stage. Optionally or alternatively, a compensation optical system such as a zoom expander including a plurality of cylindrical lenses or the like is adopted to compensate the shape (i.e., to compensate to have the circular cross section) of the beam.
In order to design and manufacture an optical system which is capable of compensating a laser beam as desired, the optical system should be designed for individual devices since the cross sectional shape of the laser beam emitted by the laser sources have individual differences. Further, even in a single device, if the laser source is replaced with another one, the compensation optical system should also be replaced according to the characteristic of the new laser source.
If the zoom expander is used, a relative inclination between the generating lines of the respective cylindrical lenses greatly affect wavefront aberration. Therefore, when the zoom expander is used, a troublesome adjustment of the zoom expander is required. Further, decentering of the cylindrical lenses when zooming is performed also causes a relatively large amount of aberration. Therefore, the compensation of the cross-sectional shape of the beam by the zoom expander is very difficult.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an improved beam shape compensation optical system capable of compensating a cross-sectional shape of various type of beams, relatively easily.
Another object of the invention is to provide an imaging device which allows a relatively simple adjustment operation for compensating the cross-sectional shape of the beam when the device is manufactured and/or when a light source is replaced.
For the above object, according to an aspect of the invention, there is provided a beam shape compensation optical system, which is provided with:
a first anamorphic beam expander which expands a cross section of a parallel beam incident along a predetermined direction at a first magnification ratio M
1
at least in a first direction which is perpendicular to the predetermined direction; and a second anamorphic beam expander which expands a cross section of a parallel beam incident along the predetermined direction at a second magnification ratio M
2
at least in a second direction which is perpendicular to the predetermined direction. The first and second anamorphic beam expander are arranged rotatable so that an angle between the first direction and the second direction on a plane perpendicular to the predetermined direction is changeable.
Since the cross-sectional shape of the incident beam can be changed in two different directions individually, and the directions are changeable, various types of elliptical shapes can be changed into a perfect circle easily.
According to another aspect of the invention, there is provided a beam shape compensation optical system, provided with:
a first beam expander which expands a cross section of a parallel beam incident along a first predetermined direction at a first magnification ratio M
1
along a first magnification axis which is perpendicular to the predetermined direction;
a first holder for holding the first beam expander such that the first beam expander is rotatable about a first axis which is parallel to the first predetermined direction;
a second beam expander which expands a cross section of a parallel beam incident along a second predetermined direction at a second magnification ratio M
2
along a second magnification axis which is perpendicular to the predetermined direction; and
a second holder for holding the second beam expander such that the second beam expander is rotatable about a second axis which is parallel to the second predetermined direction.
Optionally, the second axis may be coaxial with the first axis. With this structure, the principal ray of the incident beam and the principal ray of the beam emitted from the beam shape compensation optical system is aligned on a same line.
Optionally, M
1
×M
2
=1. If this condition is satisfied, the area of the incident beam and the area of the compensated beam are unchanged.
Alternatively, M
1
is equal to M
2
. In this case, it is not necessary to prepare beam expanders having different characteristics. In other words, only by one type of, and two beam expanders, the beam shape can be compensated.
In one example, each of the first and second beam expander includes two cylindrical lenses.
Alternatively, each of the first and second beam expander may include two prisms.
According to a further aspect of the invention, there is provided an imaging device, which is provided with: a laser source for emitting a parallel laser beam; and a beam shape compensation optical system inserted within an optical path of the laser beam for compensating a cross sectional shape of the laser beam.
The beam shape compensation optical system may include:
a first beam expander which expands a cross section of the laser beam incident along a first predetermined direction at a first magnification ratio M
1
along a first magnification axis which is perpendicular to the first predetermined direction;
a first holder for holding the first beam expander such that the first beam expander is rotatable about a first axis which is parallel to the first predetermined direction;
a second beam expander which expands a cross section of the laser beam incident along a second predetermined direction at a second magnification ratio M
2
along a second magnification axis which is perpendicular to the second predetermined direction; and
a second holder for holding the second beam expander such that the second beam expander is rotatable about a second axis which is parallel to the second predetermined direction.


REFERENCES:
patent: 5303221 (1994-04-01), Maeda et al.
patent: 5632083 (2000-05-01), Tada et al.
patent: 6064504 (2000-05-01), Minakuchi et al.
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patent: 63-125914 (1988-05-01), None
patent: 9-306108 (1997-11-01), None
patent: 9-288837 (1997-11-01), None
patent: 11-16194 (1999-01-01), None
patent: 00/00964 (2000-01-01), None
“Dual Wavelength Optical Head for 0.6 mm and 1.2 mm Substrate Thicknesse”, R. Katayama et al., Japanese Journal of Applied Physics., vol. 36, 1997, pp. 460-466, XP002133610, Tokyo, (ISSN: 0021-4922).
English Language Abstract of JP 9-288837.
English Language Abstract of JP 9-306108.
English Language Abstract of JP 11-16194.

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